Exactly what does "Re-install Now" option do?

I can’t find any documentation on what this option on the “WordPress Updates” screen actually does.

Does it reset the WordPress site to default, with the default theme, default posts, and default settings? Or does it merely re-install the core files, leaving anything added/changed alone?

I have been fiddling around with a new but non-production site, and I want to get it back to the way it was before I started doing anything. Like “out of the box” new. Will this Re-install do that?